/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.client;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.apache.yetus.audience.InterfaceAudience;
import org.apache.hadoop.hbase.util.Bytes;

/**
 * A scan result cache that only returns complete result.
 */
@InterfaceAudience.Private
class CompleteScanResultCache implements ScanResultCache {

    private int numberOfCompleteRows;

    private final List<Result> partialResults = new ArrayList<>();

    private Result combine() throws IOException {
        Result result = Result.createCompleteResult(partialResults);
        partialResults.clear();
        return result;
    }

    private Result[] prependCombined(Result[] results, int length) throws IOException {
        if(length == 0) {
            return new Result[]{combine()};
        }
        // the last part of a partial result may not be marked as partial so here we need to check if
        // there is a row change.
        int start;
        if(Bytes.equals(partialResults.get(0).getRow(), results[0].getRow())) {
            partialResults.add(results[0]);
            start = 1;
            length--;
        } else {
            start = 0;
        }
        Result[] prependResults = new Result[length + 1];
        prependResults[0] = combine();
        System.arraycopy(results, start, prependResults, 1, length);
        return prependResults;
    }

    private Result[] updateNumberOfCompleteResultsAndReturn(Result... results) {
        numberOfCompleteRows += results.length;
        return results;
    }

    @Override
    public Result[] addAndGet(Result[] results, boolean isHeartbeatMessage) throws IOException {
        // If no results were returned it indicates that either we have the all the partial results
        // necessary to construct the complete result or the server had to send a heartbeat message
        // to the client to keep the client-server connection alive
        if(results.length == 0) {
            // If this response was an empty heartbeat message, then we have not exhausted the region
            // and thus there may be more partials server side that still need to be added to the partial
            // list before we form the complete Result
            if(!partialResults.isEmpty() && !isHeartbeatMessage) {
                return updateNumberOfCompleteResultsAndReturn(combine());
            }
            return EMPTY_RESULT_ARRAY;
        }
        // In every RPC response there should be at most a single partial result. Furthermore, if
        // there is a partial result, it is guaranteed to be in the last position of the array.
        Result last = results[results.length - 1];
        if(last.mayHaveMoreCellsInRow()) {
            if(partialResults.isEmpty()) {
                partialResults.add(last);
                return updateNumberOfCompleteResultsAndReturn(Arrays.copyOf(results, results.length - 1));
            }
            // We have only one result and it is partial
            if(results.length == 1) {
                // check if there is a row change
                if(Bytes.equals(partialResults.get(0).getRow(), last.getRow())) {
                    partialResults.add(last);
                    return EMPTY_RESULT_ARRAY;
                }
                Result completeResult = combine();
                partialResults.add(last);
                return updateNumberOfCompleteResultsAndReturn(completeResult);
            }
            // We have some complete results
            Result[] resultsToReturn = prependCombined(results, results.length - 1);
            partialResults.add(last);
            return updateNumberOfCompleteResultsAndReturn(resultsToReturn);
        }
        if(!partialResults.isEmpty()) {
            return updateNumberOfCompleteResultsAndReturn(prependCombined(results, results.length));
        }
        return updateNumberOfCompleteResultsAndReturn(results);
    }

    @Override
    public void clear() {
        partialResults.clear();
    }

    @Override
    public int numberOfCompleteRows() {
        return numberOfCompleteRows;
    }
}
